Systems and methods for the control of periodic disturbances are known. For example, U.S. Pat. No. 7,952,308 discloses a method and apparatus for reducing torque ripple in a permanent magnet motor system. A torque ripple reduction signal is produced in response to a torque command and operational control signals are modified in response to the torque ripple reduction signal to generate reduced ripple operational control signals, which are provided to an inverter for control of a permanent magnet motor. The torque ripple reduction signal includes one or more predetermined harmonics of a current signal of the motor defined in response to a predetermined torque ripple characteristic of the motor. EP 1,182,771 discloses a controller for an electronically commutated electrical machine that receives a feedback signal indicative of a parameter which it is desired to minimise, for example torque ripple, current, voltage, vibration or acoustic noise. The controller computes the amplitude and phase of a set of harmonics in the parameter and sequentially injects harmonics of the correct amplitude and phase to minimise the parameter. An optimising routine iterates through the set of harmonics to further reduce the parameter.
There is a need, in particular in the context of the control of a mechanical system in which the characteristics of a periodic perturbation changes over time, of an adaptive controller for reducing periodic perturbations, which can efficiently track a changing nature of a period perturbation.